The objective of the proposed project is to develop an instrument which will generate and analyze a clinical electroretinogram and extract information which is pertinent to assessing retinal ischemia in patients with retinal vascular disease. This device will be considerably easier to operate than existing electrodiagnostic systems and will provide relevant, unambiguous information to the clinician. The device will consist of a combination ganzfeld photic stimulator and corneal electrode, associated electronics, and a microcomputer. A sinusoidally varying photic stimulus will be presented to the patient while recording the electroretinogram. Algorithms encoded in software will determine if a viable signal is being recorded, and if so, will estimate the amplitude of the signal and the relationship between phase lag and frequency. These two parameters will be presented to aid the physician in determining whether or not to treat a patient to prevent the development of the blinding complications of retinal or iris neovascularization.